Zeolite-based honeycomb body

ABSTRACT

Zeolite-based honeycomb bodies and methods of manufacturing same. Zeolite-based honeycomb bodies especially suited for engine exhaust treatment applications include a primary phase comprising a zeolite having a SiO2 to Al2O3 molar ratio in the range from 5 to 300. The zeolite-based composites are porous with an open porosity of at least 25% and a median pore diameter of at least 1 micron. The zeolite-based honeycomb bodies can be manufactured by an extrusion method.

RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 12/275,568, filed on Nov. 21, 2008, now U.S. Pat. No. 7,754,638which claims the benefit of priority to U.S. Provisional Application No.61/004,783, filed Nov. 30, 2007, entitled “Zeolite-Based HoneycombBody.”

FIELD

The present invention relates generally to zeolite-based honeycombbodies, such as for use in engine exhaust systems.

BACKGROUND

Various methods and devices are known for reducing emissions of engineexhaust, including catalyst supports, or substrates, and filters.

SUMMARY

The present disclosure relates to zeolite-based honeycomb bodies andtheir manufacture. The zeolite-based honeycomb bodies are particularlyuseful in applications of engine exhaust filtration, and moreparticularly to high porosity filters for engine exhaust systems,particularly diesel exhaust systems. The honeycomb bodies exhibit a highsurface area, high porosity, or sufficient strength for catalyticapplications, or combinations thereof, and preferably a combination ofall, while also reducing or eliminating the need for washcoating a highvolume of catalyst onto a support. In embodiments, an extrudedzeolite-based honeycomb body is provided having one or more improvedproperties of porosity, thermal and mechanical properties, particularlyunder conditions encountered in diesel exhaust system use andmanufacture.

In one aspect, an extruded zeolite-based honeycomb body is provided inaccordance with the present disclosure comprising a primary phasematerial comprising a zeolite having a SiO2 to Al2O3 molar ratio in therange from 5 to 300, wherein the honeycomb body exhibits a median porediameter of at least 1 micron, preferably at least 3 microns and morepreferably at least 5 microns.

In another aspect, an extruded zeolite-based honeycomb body is providedin accordance with the present disclosure comprising a primary phasematerial comprising a zeolite having a SiO2 to Al2O3 molar ratio in therange from 5 to 300, and preferably further comprises at least onesecondary phase material having a coefficient of thermal expansion of atleast 10×10⁻⁷/° C., wherein the honeycomb body exhibits a median porediameter measured by mercury intrusion of at least 1 micron, i.e. 1micron or greater. Preferably, the secondary phase material is selectedfrom the group consisting of alumina, zircon, zirconia, cordierite,titania, silica, ceria and other oxides of rare earth metals.

In another aspect, an extruded zeolite-based honeycomb body exhibiting acoefficient of thermal expansion of zero to +/−15×10⁻⁷/° C., preferablyzero to +/−10×10⁻⁷/° C. over the temperature range from 25° C. to 800°C., a porosity in the range of about 30-70% and a median pore size of atleast 1 micron is provided, i.e. 1 micron or greater, said honeycombbody being formed from a mixture comprising a primary phase materialcomprising a zeolite having a SiO₂ to Al₂O₃ molar ratio in the rangefrom 5 to 300; a secondary phase material having a coefficient ofthermal expansion greater than 10×10⁻⁷/° C.; a binder, and 1 to 85% byweight superaddition of a poreformer agent.

In another aspect, an extruded zeolite-based honeycomb body is providedexhibiting a surface area in the range of 20 m²/g to about 300 m²/g,preferably exhibiting a surface area of greater than about 100 m²/g,more preferably greater than about 200 m²/g; an open porosity of atleast 25%, preferably between 30% and 70%; and a median pore diameter ofat least 1 micron is provided, i.e. 1 micron or greater. In someembodiments, the median pore diameter is in the range of 1 to 25microns; in other embodiments the median pore diameter is at least 3microns; in other embodiments at least 5 microns; in other embodimentsat least 10 microns; and in other embodiments in a range of about 3-20microns.

In some embodiments, the extruded zeolite-based honeycomb bodies of thepresent disclosure also exhibit a low coefficient of thermal expansionof zero to +/−15×10⁻⁷/° C., preferably zero to +/−10×10⁻⁷/° C., over thetemperature range from 25° C. to 800° C., and may further exhibit amodulus of rupture, as measured by the four-point method on a cellularbar of rectangular cross-section cut parallel to the direction of thechannels, of at least about 200 pounds per square inch (psi), preferablyof at least 300 psi, more preferably 600 psi, and more preferably atleast 900 psi.

In another aspect, the present disclosure is directed to a method ofmanufacturing a zeolite-based honeycomb body having a median pore sizegreater than 1 micron comprising the steps of (a) forming a mixturecomprising a zeolite source material having a SiO₂ to Al₂O₃ molar ratioin the range from 5 to 300; optionally a secondary phase source materialhaving a coefficient of thermal expansion greater than 10×10⁻⁷/° C.; abinder and 1-85% superaddition of a poreformer agent; (b) extruding themixture to form a cellular body; and (c) heating the cellular body toproduce a zeolite-based honeycomb body. In some embodiments, the methodincludes first providing a batch slurry mixture comprised of sourcematerials for the primary phase zeolite component and optionally asecondary phase material; spray-drying the slurry mixture to formgenerally uniformly sized spray-dried agglomerates with a more uniformparticle size distribution (where here the “particle size” refers to thesize of the agglomerates); forming a batch extrusion mixture from thespray-dried agglomerate; extruding the batch extrusion mixture to form acellular body; and heating the cellular body to form a zeolite-basedhoneycomb body.

In some embodiments, the extruded zeolite-based honeycomb bodiesprovided in accordance with the present disclosure are especiallysuitable in applications for treating diesel and lean burn engineexhaust.

Additional features and advantages of the present disclosure will be setforth in the detailed description which follows, and in part will bereadily apparent to those skilled in the art from that description orrecognized by practicing the subject matter as described herein,including the detailed description which follows, the claims, as well asthe appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description present particular embodiments, andare intended to provide an overview or framework for understanding thenature and character of the inventions as claimed. The accompanyingdrawings are included to provide a further understanding of thedisclosure, and are incorporated into and constitute a part of thespecification. The figures illustrate various embodiments and aspects ofthe disclosure, and together with the description serve to explain theprinciples and operations of the claimed invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graphic illustration of the pore size distribution (logdifferential intrusion of ml/g vs. pore size in units of microns) for azeolite/alumina body formed from a batch with 10% green bean starchsuperaddition.

FIG. 2 is a graphic illustration of the pore size distribution (logdifferential intrusion of ml/g vs. pore size in units of microns) for azeolite/alumina body formed from a batch with 30% green-bean starchsuperaddition.

FIG. 3 is a graphic illustration of the pore size distribution (logdifferential intrusion of ml/g vs. pore size in units of microns) for azeolite/cordierite body formed from a batch with 83% graphitesuperaddition.

FIG. 4 is a graphic illustration of the pore size distribution (logdifferential intrusion of ml/g vs. pore size in units of microns) for azeolite/cordierite body formed from a batch with 50% potato starchsuperaddition.

FIG. 5 is a graphic illustration of the pore size distribution (logdifferential intrusion of ml/g vs. pore size in units of microns) for azeolite/cordierite body formed from a batch with 50% potato starchsuperaddition.

FIG. 6 is a graphic comparison illustration of thermal expansion over arange of 25-800° C. of exemplary zeolite-based bodies and a commercialcordierite body.

DETAILED DESCRIPTION

Reference will now be made in detail to the embodiments of thedisclosure, examples and aspects of which are illustrated in theaccompanying drawings.

The values d₁₀ and d₅₀ are defined as the pore diameters at 10% and 50%of the cumulative pore size distribution based upon volume, as measuredby mercury porosimetry, with d₁₀<d₅₀. Thus, d₅₀ is the median porediameter, and d₁₀ is the pore diameter at which 10% of the pores arefiner, based upon volume. The value of d₉₀ is the pore diameter forwhich 90% of the pores, by volume, are finer in diameter; thusd₁₀<d₅₀<d₉₀. The value d_(F) is defined as (d₅₀−d₁₀)/d₅₀. The valued_(B) is defined as (d₉₀−d₁₀)/d₅₀. Unless otherwise noted herein,particle size measurements herein were made with a Microtrac Inc.particle size analyzer device.

One aspect of the present disclosure is directed to extrudedzeolite-based honeycomb bodies. Embodiments of the extrudedzeolite-based honeycomb bodies of the present disclosure can beparticularly suited for use as flow through substrates or as exhaustfilters such as in diesel exhaust and lean burn exhaust systems. Thehoneycomb bodies of the present disclosure preferably exhibit highsurface area and low thermal expansion, and in some embodiments reduceor eliminate the need for excessive high surface area washcoating.Filters described are referred to as “wall flow” filters because theflow paths resulting from channel plugging require the exhaust beingtreated to flow through the porous cell walls prior to exiting thefilter. Embodiments of the zeolite-based honeycomb bodies disclosedherein preferably exhibit thermal stability at temperatures up to atleast 800° C. such that the components of the microstructure do notsubstantially change in composition or physical structure.

Honeycomb bodies provided in accordance with the present disclosurecomprise a ceramic honeycomb body comprising a primary phase comprisingone or more zeolite components. Exemplary zeolites for inclusion in anextrudable batch include ZSM-5, Beta, Mordenite, Y-zeolite,Ultrastable-Y and aluminum phosphate zeolites, and mixtures thereof. Onesource of ZSM-5 zeolite is supplied by Zeolyst International of ValleyForge, Pa. The zeolite material preferably has a SiO₂ to Al₂O₃ molarratio in the range from about 5 to about 300, more preferably about 25to about 60. The primary phase zeolite, or mixture of zeolites,preferably have a mean particle size in the range of about 10 to about100 microns. The primary phase material may comprise about 35% to about80% (volume percent) of the fired zeolite-based composite filter bodycomposition. Material for use in formulating the primary phase materialuseful in producing the extruded zeolite-based bodies of the presentdisclosure may be selected from any suitable source.

In some embodiments, the walls of the honeycomb body disclosed hereinmay advantageously incorporate an active catalyst (such as one or morecombinations of metals from the transition metals, alkali and alkalineearth metals or the lanthanides) dispersed throughout (i.e. within) thewall for controlling emissions components. The catalyst(s) (e.g. metalcations) may be impregnated in the zeolite materials by the zeolitesupplier or manufacturer; such pre-impregnated powders can then be mixedinto an extrusion batch. In other embodiments, the catalyst(s) may beloaded into the zeolite by mixing the catalyst(s) into an extrusionbatch comprising a zeolite, or the catalyst(s) may be loaded into thezeolite by mixing the catalyst(s) into a slurry comprising a zeolite,wherein the slurry is spray-dried to form agglomerates. Thus, thecatalyst(s) can be integrated into the honeycomb bodies by impregnatingpre-extrusion zeolite material in the extrusion batch formulation and/orduring spray-drying. At the time of batch formulation and extrusion,catalyst(s) can readily be incorporated in the zeolite powders toproduce an extruded body with added catalyst functionality.Advantageously, the catalyst materials may be integrated into theextruded body, thereby reducing the need for additional high surfacearea washcoat treatments. In some embodiments, the integrated catalystfunctionality can reduce the need to use washcoat treatments for thecatalyst application and thereby can simplify the processing of thecomposite bodies, potentially reducing manufacturing cost and time. Insome embodiments, the integrated catalyst functionality can thus lessena washcoat treatment requirement, and may also lower backpressures whencompared to known filter bodies which require thick washcoat treatments.However, in some embodiments, an additional catalyst washcoat treatmentmay also be subsequently applied to the extruded body to impart desiredenhanced performance.

Active metal catalyst(s) can be selected from the group consisting ofFe⁺², Cu⁺², W⁺², Co⁺², Mn⁺², Ag⁺¹, Zr⁺¹, Mo⁺², Rh⁺², Ni⁺², Pt⁺², La⁺²,and Ce⁺², and combinations thereof. Derivatives of the metal salts,nitrates, acetate and carbonate may be used for the exchange process. Insome embodiments, the iron cation is introduced as Fe⁺² from theprecursor to increase the effectiveness of the exchange process. Ferrousammonium sulphate is an exemplary Fe⁺² source that may be used toproduce high SCR activity. Thus, pre-exchanged or impregnated powdersmay be used. In some embodiments, the active metal(s) do not exceed 10%by weight, based on the total weight of the finished honeycomb body. Insome embodiments, the catalyst(s) loading is in the range of about 1 toabout 6% by weight. When the honeycomb body is deployed in an SCRapplication, preferably each of the one or more metal(s) is deposited inthe zeolite pores, as excess metal(s) on the surface may degrade the SCRactivity. In some embodiments, one or more alkali (potassium, lithium,sodium and cesium) and alkaline (barium, calcium) earth metals may beincorporated in the extrusion composition to provide a honeycomb bodyhaving an active NOx adsorber capability. Without being held to anyparticular theory, it is expected that the issue of alkali metalmigration is not as far-reaching as encountered with known washcoats ona ceramic substrate, such as cordierite substrate, if the alkali oralkaline earth metals are substantially disposed within the zeolitepores.

In another aspect, the extruded zeolite-based honeycomb bodies of thepresent disclosure preferably further include at least one secondaryphase material selected from a material having a coefficient of thermalexpansion of at least 10×10⁻⁷/° C., The secondary phase material ispreferably thermally stable at temperatures up to at least 800° C.,preferably at least 1000° C. such that the honeycomb body does notsubstantially change in composition and physical structure. Thesecondary phase materials may include those materials that furtherexhibit high surface area greater than 20 m²/g, preferably greater than100 m²/g, and more preferably greater than 200 m²/g. The secondary phasematerials are preferably selected from alumina, zircon, zirconia,silica, cordierite titania, ceria and other oxides of rare earth metals,and combinations and mixtures thereof. In some embodiments, thesecondary phase has a mean particle size comparable to the mean particlesize of the primary phase, and is preferably in the range of up to 100microns, preferably greater than 10 microns. The secondary phasematerial has a positive coefficient of thermal expansion which balancesthe negative coefficient of thermal expansion of the primary phasezeolite material. The secondary phase material may be present in thefired ceramic body in a range of 0 to 50% (volume). In some embodiments,the secondary phase material comprises between 10 and 45% of the firedceramic body.

In another aspect, the zeolite-based honeycomb bodies also incorporate abinder component. In a further aspect of the disclosure, the secondaryphase material and binder material may be the same material. Thepermanent binder assists in providing permanent bonding strength betweenthe primary and secondary phase particles. Suitable binder materialsinclude silica or silica forming materials, as well as colloidalmaterials providing sources of alumina, cordierite, ceria and zirconia,and mixtures thereof. The colloidal materials generally may have meanparticle sizes of less than 100 nm. Mixtures or combinations of bindermaterials may also be used. The binder is preferably selected formsilicone binding agents such as silicone resins and/or emulsions. Thesecan be provided as precursors, for example, silica precursors such assilicone resin, or colloidal silica are suitable. Preferably, the binderis incorporated in the form of a silicone resin or silicone emulsion.Silicone resins can be added to the mixture in the form of an aqueousemulsion, and are commercially available, such as Wacker AG SILRES® M 50E (an emulsion of a methyl silicone resin with reported solids contentof 52-55%) or Wacker AG SILRES® M 97 E, both available formWacker-Chemie GmbH of Munich, Germany. In some embodiments, the binderis incorporated in the batch mixtures such that the fired ceramiccontains silica binder in an amount ranging from about 5 to about 30% byweight, preferably 15-30%, and more preferably about 20%. The amounts ofthe binders are based on the expected weight after heat-treatment whichwill be the weight of the binder in the product body. For example whensilicone resins are used, the weight of the binder in the product is theweight of silica added via the resins.

Advantageously, the walls of the zeolite-based honeycomb bodies of thepresent disclosure have a high porosity after firing of not less than25% and preferably in the range of about 30-70% and a mean pore size ofat least 1 micron. In some embodiments, the median pore diameter is atleast 3 microns, more preferably at least 5 microns and is mostpreferably in the range of about 3 to about 20 microns. In someembodiments, the median pore diameter is at least 10 microns or more,and can be selected to be in the range of about 5 to 25 microns. Theporosity and median pore diameter can be controlled by incorporating aporeformer into the batch mixture prior to extrusion, as well asutilizing larger inorganic particle components. In another aspect, thepercentage of pores having a diameter greater than 5 microns is at least10%, preferably at least 20%, more preferably at least 30% and even morepreferably at least 40%. The poreformer may be selected from graphite,starches, including green bean starch, potato starch, rice hulls, foams,and mixtures thereof. The poreformer is preferably selected fromporeformer particles having a size in the range of about 10 to about 70microns, and more preferably 20 to 50 microns. The poreformer isincorporated in the pre-extruded batch mixture in an amount ranging fromabout 1 to about 85% by superaddition, more preferably in the range ofabout 10 to about 60%. In some embodiments, the poreformer agent ispresent in the green honeycomb body in a range from 10% to 40% by weightsuperaddition. The poreformer in the mixture is calculated as asuperaddition over the combined weights of primary phase material,secondary phase material and binder (based on as-heated yield) accordingto the following formula: (wt. poreformer/wt. of primary phasematerial+secondary phase material+binder)×100

Embodiments of the disclosed structures exhibit advantageous openporosity, median pore sizes, permeability and mean coefficients ofthermal expansion. Exhaust filtration embodiments can have a porosity ofat least 30-70%, and a median pore diameter as measured by mercuryintrusion of at least 1 micron, preferably at least 3 microns, morepreferably at least 5 microns and preferably in a range of about 3-20microns. The porosity and median pore diameter can be controlled bycontrolling the size of the inorganic particle precursors, as well asthe size and amount of selected poreformers. The primary phase zeolitematerials include micropores that form microchannels through the zeoliteparticles. The microporosity and microchannels of the zeolite materialsadd further connectivity between adjacent honeycomb channels that arebelieved to lead to lower system backpressure in filter applications.

In some embodiments, the zeolite-based honeycomb bodies exhibit a highsurface area in the range of 20 m²/g to about 300 m²/g, preferablyexhibiting a surface area of greater than about 100 m²/g, and an openporosity of at least 30%, preferably between 30% and 70%. The highporosity and median pore diameter, as well as the high surface area,allow for catalyst integration and thereby reduces need for excessivewashcoating, which may lead to a lower pressure drop in thezeolite-based honeycomb bodies of the present disclosure.

In another aspect, the disclosed zeolite-based honeycomb bodies alsoexhibit a mean coefficient of thermal expansion from 25-800° C. in therange of about 0 to +/−15×10⁻⁷/° C., preferably +/−10×10⁻⁷/° C., and amodulus of rupture as measured on a cellular bar of at least about 200pounds per square inch (psi), preferably at least about 300 psi, morepreferably at least about 600 psi, and more preferably at least about900 psi. For zeolites to be used as monolithic honeycombs and used athigh temperatures (>300° C.), these materials need to have sufficientthermal shock resistance. Thermal shock resistance depends on thecoefficient of thermal expansion. The closer the coefficient of thermalexpansion is to zero, the more thermally shock resistant is thematerial. Zeolites have low or negative thermal expansions, that is, acoefficient of thermal expansion (CTE) of −20×10⁻⁷/° C. or even lowerover their useful stable temperature ranges. The secondary phasecomponent preferentially has a higher thermal expansion than thezeolite-based primary phase components, preferably exhibiting a positiveCTE value. The secondary phase component raises the thermal expansion ofthe primary phase zeolite or zeolite mixtures over the useful stabletemperature ranges. The primary and secondary phase combinations of thepresent disclosure and the products produced therefrom therefore havecoefficients of thermal expansion (CTE's) which are higher than theCTE's of the zeolite materials without the secondary phase component.Advantageously, embodiments of zeolite-based honeycomb bodies describedherein include a secondary phase material having a positive thermalexpansion coefficient that balances the negative coefficient of theprimary phase. Thus, embodiments of the present disclosure providethermally shock resistant zeolite-based honeycomb bodies and methods ofmaking them.

The general method of producing porous honeycomb bodies comprises mixingbatch materials, blending the mixture, forming a green body, andsubsequently sintering the green body to a hard porous structure. Abatch mixture suitable for extrusion can be prepared by mixing the drybatch with a suitable liquid vehicle. The vehicle may comprise water andextrusion aids necessary to give the batch plastic formability andsufficient green strength after forming to resist breakage prior tofiring. Preferably, the amounts of primary phase material and secondaryphase material in the mixture will be essentially the same as theamounts in the product body; in some embodiments, the mixture is made upin parts by weight based on the desired final ceramic body: from 20 toabout 80% of primary phase zeolite material, up to about 60% of thesecondary phase material, and about 10 to 50% of the permanent binder(based on the expected weight after heat treatment). These amounts aresubstantially the same as the levels in the finished honeycomb bodies.Various lubricants, binders, surfactants, pore-formers and viscositymodifiers are added to the batch during the mixing step to provideviscosity control, plasticity and strength prior to firing, and porosityto the fired structure.

In some embodiments, a method of manufacturing the zeolite-basedhoneycomb body includes the steps wherein the primary phase material,and preferably a secondary phase material is mixed in a liquid vehicleto form a slurry. Thereafter, the slurry is spray-dried, or similartechniques are used, to form agglomerates comprised of the initialmaterial(s) as an additional process step to mix the materials, increasethe particle size (i.e. agglomerated particle, or agglomerate, size) andobtain a more uniform size distribution of the agglomerates prior toextrusion and firing. The spray-drying forms agglomerates of thespray-dried components, preferably including the primary phase zeolite,secondary phase material and permanent binder. The agglomerates can beheated to form calcined agglomerates or the agglomerates can be useddirectly after spray-drying, which may then be used in forming anextrusion batch mixture.

A method of making a honeycomb body is disclosed herein, the methodincludes mixing zeolite source material as herein described with apermanent binder source material and forming zeolite agglomerates fromthe mixture. The agglomerates may further include a secondary phasesource material. The agglomerates may also be calcined prior tosubsequent use. The zeolite agglomerates are then mixed with a poreformer or mixture of pore formers and a temporary binder to form anextrudable mixture. The extrudable mixture is extruded to form ahoneycomb body comprised of a plurality of walls defining channels. Thehoneycomb body is then heated to produce a honeycomb body having aprimary phase zeolite material homogenously distributed therein, amedian pore diameter greater than 1.0 micron and a porosity greater than25% in the walls. A portion of the channels may be plugged, for exampleby known plugging methods, to form a wall-flow filter. In anotheraspect, a secondary phase source material may be mixed with the zeoliteagglomerates and permanent binder source material to form the extrudablemixture and then further processed as outlined above to form a honeycombbody having a primary phase zeolite material and a secondary phasematerial homogenously distributed therein, a median pore diametergreater than 1.0 micron and a porosity greater than 25% in the walls.

In some method embodiments, a primary phase zeolite source material, asecondary phase source material and binder are mixed into slurry andsubsequently spray-dried together to increase the mean particle size ofthe resultant spray-dried agglomerate above the mean particle size ofthe combined constituent materials. In some embodiments, the meanparticle size of the spray-dried agglomerate is at least 10 microns, andpreferably in the range of 10 to 100 microns, more preferably in therange of 20-50 microns, and in some embodiments in the range of 25-45microns. The agglomerates of the spray-drying may be calcined. Theagglomerates are combined with suitable amounts of permanent binder,poreformer, organic paste and processing aids and formed into desiredstructures, such as a honeycomb structures, by extrusion. Thespray-drying advantageously provides larger inorganic particles that mayprovide increases in porosity and median pore diameter of the resultantceramic body.

The extrusion aids can comprise binders and plasticizers/paste formers,as well as processing aids such as lubricants. The organic pasteprovides plasticity during forming, and some strength to the extrudedbody prior to firing. Organic pastes suitable for the purposes set forthherein include cellulose ether type materials and/or their derivatives.Sources of cellulose ethers and/or derivatives thereof include theMethocel™ line of cellulose ethers, from Dow Chemical Co., and mixturesthereof. Methylcellulose is an example of an organic paste forming agentsuitable for use in formulating the filter bodies of the presentdisclosure. The organic paste and other processing aids can be added asa super addition over the combined weight of the primary phase,secondary phase and binder (based on expected weight after heattreatment). The super addition of organic paste can be in the range ofabout 3-8%, but more or less may be utilized. The organic paste ortemporary binder material is substantially burned off during thesubsequent firing of the honeycomb body. Water may be added to the batchcomponents to achieve the necessary plasticity for handling andextrusion. Water-based binders can be used for ease of processing inthis regard. The mixtures preferably also contain superaddition of aporeformer or mixtures thereof, as described above, to assist incontrolling the porosity and mean pore size of the fired product.

In one illustrative embodiment, a primary phase is selected as ZSM-5zeolite having an SiO₂ to Al₂O₃ ratio of 55 to 1. The median particlesize of the zeolite is approximately 10 microns. A secondary phasematerial is selected as calcined A16 α-alumina having a median particlesize of less than 1 micron. The primary phase and secondary phasematerials were prepared in slurry form comprising approximately 28.9%(mass) zeolite, approximately 12.4% α-alumina and approximately 17.3% ofa silicon resin emulsion and approximately 16.1% ethylene acrylic acidemulsion in water. The slurry was spray-dried and the resultingagglomerates were calcined to 850° C. The median particle size of theresulting spray-dried and calcined agglomerate was approximately 26.2microns. The calcined agglomerates are further mixed with suitableamounts of binder, paste, poreformer, water and processing aids to forman extrudable composition and extruded.

One method of forming honeycomb bodies is by extrusion through a formingdie. A ram extruder, continuous auger, or twin screw extruder or otherknown extrusion apparatus can be used. The honeycomb body according tothe present disclosure can have any convenient size and shape, forexample, a right circular cylindrical shape structure. The honeycombbody can be extruded to form a matrix of walls wherein the primary phasematerial(s), secondary phase material(s) (if present) and permanentbinder are homogenously distributed throughout the walls. The matrix ofwalls define channels extending through the honeycomb body. Thehoneycomb body can be further coated with a skin material at the outerperiphery of the structure as is known in the art.

The firing procedure can be achieved with known ovens, such as periodic(or batchwise) ovens, or kilns, such as tunnel kilns that employ one ormore conveyors. In some embodiments, the green structures are fired byexposing the green structures to a heated gaseous environment, such asair, wherein the air is heated to temperatures in the range of about400° C.-1200° C., and in some of these embodiments between about 600°C.-900° C., with a residence time in that temperature range of aduration sufficient to complete firing of the body. The residence timecan be about 1 to 10 hours, and in some embodiments from 3 to 6 hours,and may depend, for example, on the type or source of componentsemployed.

In some of embodiments, the honeycomb body is a flow through substrate.In some embodiments, the honeycomb body is a wall flow filter, such as aparticulate filter, for example a diesel particulate filter. In filterembodiments, at least a portion of the channels or cells are plugged soas to seal the respective cell channels in the so-formed zeolite-basedhoneycomb body. For example, in some embodiments a portion of the inletend cell channels are plugged and a portion of the outlet end cellchannels are plugged but not corresponding to those at the inlet end,such that each cell is plugged at one end only. Plugging at the ends ofthe cell channels is preferably accomplished with plugs having a depthless than about 20 mm, and in some embodiments about 5 to 20 mm. In someembodiments, the plugging arrangement is to have every other cellchannel on a given end plugged in a checkered pattern.

The disclosure may be further understood by reference to the followingExamples, which are intended to be merely illustrative of the presentlypreferred compositions and method for carrying out the invention.

EXAMPLE 1 Preparing Zeolite-Based Agglomerates

Zeolite agglomerates were prepared by forming a slurry composition asoutlined in Table 1 below. Optional calcining was performed on slurriesof Batches 1 and 2 to form an agglomerate having the final compositionand properties outlined in Table 2, where particle size refers to thesize of agglomerates. All percentages are mass % based on the total massof the composition.

TABLE 1 Batch 1 Batch 2 Batch 3 Slurry Slurry Slurry ZSM-5 28.9% 16.9%16.2% A16SG 12.4% — — alumina Cordierite — 24.4% 23.3% (500 mesh)Silicone 17.3% 17.3% — resin* Colloidal — — 57.7% silica** EAA 16.1%16.1% — emulsion*** DI**** 25.3% 25.2%  2.9% *= silicone resin emulsion(Wacker Silres M50E) **= Ludox ® SK-B colloidal silica ***= ethyleneacrylic acid emulsion ****= deionized water. Additional water may beadded as necessary for slurry viscosity control.

TABLE 2 Batch 1 Batch 2 Batch 3 Agglomerate Agglomerate AgglomerateZSM-5 59.5% 34.9% 30.0% A16SG 25.5% — — alumina Cordierite — 50.2% 43.2%(500 mesh) Silica 15.0% 15.0% 26.8% binder Median 26.2 34.4 46 ParticleSize (microns) 10% < 8.7 16.6 22 than* (microns) 90% < 47.1 85.2 115than** (microns) *= 10% of particles fell below **= 90% of particlesfell belowThe Batch 1 and Batch 2 slurries were calcined to 850° C. afterspray-drying, while Batch 3 was not calcined. The Batch 3 spray-driedagglomerate was subsequently screened to remove particles above 500 meshand below 60 mesh. Particle size data for Batch 3 in Table 2 is afterscreening.

EXAMPLE 2 Preparing Extruded Zeolite-Based Honeycomb Bodies

Extruded zeolite-based honeycomb bodies were prepared from thezeolite-based agglomerate batches of Example 1 to form the extrusionbatch compositions outlined in Table 3. All percentages are mass %. Moreor less water may be added to the extrusion batch formulations asnecessary for rheology control. The resulting extrusion batchcompositions were extruded into honeycomb cellular bodies having about200 cells per square inch, and having a wall thickness of about 16 mils.

The extruded cellular bodies were next dried and then fired in air tomaximum oven temperatures of 850° C. and held there for approximately 3hours to form the final product structure. The structures were thenevaluated for physical properties. Percent porosity, and median porediameters were determined by mercury porosimetry. The measuredproperties of the extruded zeolite-based honeycomb bodies of Table 3 areprovided in Table 4.

TABLE 3 Extrusion Batch 1 2 3 4 5 Batch 1 54.4% 46.0% — — — AgglomerateBatch 2 — — 40.0% 46.1% — Agglomerate Batch 3 — — — — 46.1% Agglomeratemethylcellulose  4.2%  4.2%  2.8%  3.2%  3.2% Silicone resin 36.0% 36.0%24.1% 27.7% 27.7% emulsion Green-bean  5.4% 13.8% — — — starch A625graphite — — 33.2% — — potato starch — — — 23.0% 23.0%

TABLE 4 Extrusion Batch 1 2 3 4 5 Fired Body Composition ZSM-5 46.6%44.8% 27.8% 27.8% 24.0% Alumina 20.0% 19.2% — — — Cordierite — — 40.0%40.0% 34.5% Silica binder 33.5% 36.0% 32.1% 32.1% 41.5% Porosity Data(Hg-intrusion) Porosity 43.1% 48.4% 69.6% 54.6% 54.4% Median pore 3.7 4.7  3.1 13.1 18 diameter, d₅₀ (microns) d₁₀ 0.58 1.37 1.03 1.56 1.19d₉₀ 8.51 9.03 55.32 30.27 23.39 d_(F) 0.84 0.71 0.67 0.88 0.93 d_(B)2.14 1.63 17.51 2.19 1.23 Porosity over 5   11%   22% 31.0%   42%   44%micronsFIGS. 1-5 respectively depict log differential intrusion versus poresize for the fired bodies from extrusion batches 1-5. FIGS. 1 and 2exhibit bi-modal pore distributions, while FIGS. 3-5 exhibit mono-modaldistributions. Each of FIGS. 1-5 depict narrow pore distributions thatindicates selective pore distributions may be achieved.

EXAMPLE 3 Evaluation of Coefficient of Thermal Expansion

Further zeolite-based bodies were prepared to test thermal expansioncharacteristics. The extrusion batch formulations are presented in Table5 below. Porosity data was determined as noted above. Mean coefficientsof thermal expansion (CTE) from 25° to 800° C. (expressed in units of °C.⁻¹) were measured using a dilatometer. Values are provided in masspercentages based on the total mass of the batch composition. More orless water may be added as necessary for extrusion rheology control.Honeycomb bodies were extruded from the batches, the bodies were dried,then fired at approximately 850° C. for three hours.

TABLE 5 Batch 6 7 8 9 Zeolite (ZSM-5) 59.9% 45.3% 34.5% 26.0% Alumina —18.5% — — Cordierite — — — 37.4% Zircon 33.1% — Silicone resin 36.1%32.5% 29.1% 32.9% emulsion Methylcellulose  4.0% 3.7% 3.3% 3.7% FiredBody Composition Zeolite 79.8% 58.5% 43.2% 33.7% Alumina — 23.9% — —Cordierite — — — 48.4% Zircon — — 41.5% — Silica binder 20.2% 17.6%15.3% 17.9% Porosity (Hg-intrusion) Porosity (%) 37.4 36.7 36.3 38.0Median pore 0.7 0.6 0.6 0.9 diameter, d₅₀ (microns) d₁₀ 0.42 0.08 0.330.28 d₉₀ 0.97 0.83 0.80 1.18 d_(F) 0.39 0.78 0.08 0.27 d_(B) 0.77 2.051.30 2.37 Porosity over 5   1% N/A N/A N/A microns

In some embodiments, d₅₀ is at least 0.5 micron; in other embodiments,d₅₀ is at least 1 micron; in other embodiments, d₅₀ is at least 3microns; in other embodiments, d₅₀ is at least 10 microns. In someembodiments, d₅₀ is between 0.5 and 25 microns. In some embodiments, d₅₀is between 0.5 and 5 microns; in some of these embodiments, thehoneycomb body is a flow through substrate. In some embodiments, d₅₀ isbetween 5 and 25 microns; in some of these embodiments, the honeycombbody is a wall flow filter, such as a particulate filter, for example adiesel particulate filter. In some embodiments, d₁₀ is less than 2.0microns; in other embodiments, d₁₀ is less than 1.5 microns; in otherembodiments, d₁₀ is less than 1.0 microns; in other embodiments, d₁₀ isless than 0.5 microns; in other embodiments, d₁₀ is less than 0.1microns. In some embodiments, porosity is greater than 45%; in otherembodiments, porosity is greater than 50%; in other embodiments,porosity is greater than 60%. In some embodiments, the honeycomb body isa wall flow filter, such as a particulate filter, having (a) a porositygreater than 40%, (b) d₅₀ less than 25 microns (and in some of theseembodiments between 10 and 25 microns), (c) d_(F) not more than 1.0micron, (d) d_(B) less than 3.0 microns, or (e) d₉₀ not more than 50microns, and preferably a combination of at least two of (a)-(e), morepreferably a combination of at least three of (a)-(e), even morepreferably a combination of at least four of (a)-(e), and still morepreferably all five of (a)-(e). In some embodiments, the honeycomb bodyis a flow through substrate having a porosity between 25 and 40%, andd₅₀ between 0.5 and 3 microns.

Referring now to FIG. 6 therein illustrated is a comparison plot of thethermal expansion over the temperature range of approximately 25-800° C.of the honeycomb bodies of Table 5 (zeolite 10, zeolite alumina 20,zeolite cordierite 30, zeolite zircon 40) with the thermal expansion ofa commercially available ground cordierite material 50. The meancoefficients of thermal expansion (CTE) from 25° to 800° C. for thebodies fired from Batches 6, 7, 8, and 9 were −16.0×10⁻⁷° C.⁻¹,−7.5×10⁻⁷° C.⁻¹, 0.0×10⁻⁷° C.⁻¹, and −1.0×10⁻⁷° C.⁻¹, respectively, andthe CTE_(25-800° C.) for the commercially available cordierite materialwas −2.6×10⁻⁷° C.⁻¹. As is illustrated, the addition of the secondaryphase materials improves the overall thermal expansion characteristicsof the zeolite bodies. Notably, the zeolite/cordierite body exhibitsalmost no hysteresis. In some embodiments, the magnitude of thecoefficient of thermal expansion is less than 16×10⁻⁷° C.⁻¹, and evenless than 12×10⁻⁷° C.⁻¹, and even less than 10×10⁻⁷° C.⁻¹ for alltemperatures between room temperature and about 800° C.; for example,the maximum magnitude of the coefficient of thermal expansion thehoneycomb body formed from Batch 9 is 8×10⁻⁷° C.⁻¹ for all temperaturesbetween room temperature and about 800° C.

In some embodiments, the zeolite based honeycomb body is washcoated witha catalyst material.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the present disclosurewithout departing from the spirit and scope of the invention. Thus it isintended that the present invention cover the modifications andvariations of this disclosure provided they come within the scope of theappended claims and their equivalents.

1. A method of making a zeolite-based honeycomb body, the methodcomprising: forming a mixture comprising a zeolite having a SiO₂ toAl₂O₃ molar ratio in the range from 5 to 300; a secondary phase materialhaving a coefficient of thermal expansion greater than 10×10⁻⁷/° C.; apermanent binder; and 1-80% superaddition of a poreformer agent;extruding the mixture to form a cellular body having a matrix of walls;and heating the cellular body to produce a zeolite-based honeycomb body;wherein the zeolite, secondary phase material and binder are first mixedto form a slurry and the slurry is spray-dried to form zeolite-basedagglomerates.
 2. The method of claim 1, wherein the walls exhibit aporosity of at least 25% and a median pore diameter of at least 1micron.
 3. The method of claim 1, wherein the zeolite is selected fromthe group consisting of ZSM-5, beta-zeolites, mordenite, Y-zeolites,ultrastabilized Y-zeolites, aluminum phosphate zeolites and mixturesthereof having a mean particle size of at least 10 microns.
 4. Themethod of claim 1, wherein the poreformer is present in the mixture as a10-60% superaddition.
 5. The method of claim 1, wherein the permanentbinder is derived from silicone resin or colloidal material selectedfrom silica, alumina, cordierite, ceria, zirconia and mixtures thereof.6. A method of making a zeolite-based honeycomb body, the methodcomprising the steps of: forming a slurry mixture comprising a zeolitematerial; spray-drying the slurry mixture to form zeolite-basedagglomerates; forming a batch formulation comprising the zeolite-basedagglomerates, a binder and a poreformer agent; extruding the batchformulation to form a honeycomb body having a matrix of walls having thezeolite material homogenously distributed therein; and heating thehoneycomb body to remove the poreformer agent to produce a median porediameter greater than 1 micron and a porosity greater than 25% in thewalls.
 7. The method of claim 6, wherein zeolite-based agglomerates arecalcined prior to incorporation into the batch formulation and theagglomerates have a mean particle size of at least 10 microns.
 8. Themethod of claim 6, wherein the slurry mixture further comprises asecondary phase material and binder.